Acoustic Architecture

Engineers study the acoustics of Raleigh’s new cathedral to ensure that voice and music can be heard and understood.

RALEIGH — Holy Name of Jesus Cathedral is an impressive sight. Its copper-covered dome shines in the sun. The cross atop the dome, standing at more than 200 feet in the air, is a new addition to the city skyline. The red brick and sandstone design, complete with a bell tower, are complementary to the architecture at NC State’s nearby Centennial campus. 

While the artistic design of the building alone could be discussed at length, this story is about acoustics: how do you hear and understand the sound that is so important to the worship experience in the Catholic Diocese of Raleigh’s new cathedral? It is an important building to the growing diocese, which extends from Raleigh to the coast. The church will be the seat of the Bishop. Bishop Michael Burbidge, who began the cathedral building project, admits that being able to understand the speakers and the music during a mass is crucial. 

“One of the biggest priorities for me is the acoustics, the sounds, because you have a very big building here, and you have to be careful with the acoustics which means the organ and the spoken word,” explains Bishop Burbidge. “Because if you have this beautiful building and people can’t hear that would be a frustration, so we are very invested in using the best technology to make sure the sound is perfect.” 

Every inch of the 2,000 seat cathedral is studied for its acoustic properties; from the size of the worship space, to the arches that top the walls and run the length of the building. Special attention is paid to the more than 200-foot high dome, the soaring altar beneath the dome, as well as the transepts or wings of the cathedral. There are plenty of angles and corners in the massive building that need to be taken into consideration as well. 

In addition to the architecture, the sound absorption and reflectivity of the building materials that will cover the interior are also analyzed. That’s because the acoustic properties of the marble that will cover the floors differs from the layers of sheet rock on the walls. And multiple layers of sheet rock absorb sounds differently than one layer. 

It all plays a part in making the new cathedral come acoustically alive. 

“When you look at all of the construction materials, the size of the space, how many people will be in the space, the material of the pews—everything effects sounds,” says Frank Yarborough, president of Avcon, an audio consulting firm with the diocese. “The challenge becomes that all of those factors either benefit or become a hindrance to achieving what you ultimately want, which is speech clarity, and then you can layer in the music.”  

Acoustical consultants who design a variety of venues all agree that while music can fill a worship space and wrap people in a kind of sound blanket, understanding the spoken word is most important. 

“When you design technology into a space, either for audio or visual support, you are affecting and affected by so many things, especially in a facility like this,” adds Yarborough. “But, speech is the number one item. Because if you can’t hear something well, and hear it intelligently, then what’s the point?” 

Once engineers understood the acoustic environment of the cathedral, they designed an acoustic model. The sound properties of every seat in the cathedral, when it is filled, are analyzed. 

The model looks like a simple, 3D line drawing of the outline of the building. There are thousands of tiny red lines inside, each line representing a person sitting in a spot in the pew. 

“All of those lines have little faces, and each side of the face has a material assigned to it and the sound absorption properties assigned to it,” says Joe Bridger, an acoustical consultant with Stewart Engineering. “You can look at any sound and see how it will be absorbed and reflected off of each person as well as all of the materials around them. 

"The program also looks at a concept called scattering, which is how much sound hits the materials and continues like you are shooting pool, and how much is scattered in every direction. In very simple terms, you could call it an echo." 

Once the acoustic model is finished, voices and choirs are recorded in a specially designed studio. The recording is then plugged into a computer program, which allows acoustical engineers to virtually hear how something would sound at any point in the cathedral. 

“It will trace the sound for where you are sitting, which in this case happens to be about half-way back in the nave, which is the central aisle of the cathedral,” says Bridger, looking at an outline drawing of the cathedral from above. There’s a star in a sea of red line "people" sitting in the pews. 

“So it traces the sounds throughout the room; it gets absorbed and scattered until it arrives at that location,” adds Bridger. “It takes all of that information and puts it into an echogram and then you can hear what it would sound like.” 

All of that information determines the type of sound system required for people to hear and understand the spoken word, as well as direct the music. 

Acoustic consultant Fred Schafer unrolls an architectural drawing of the cathedral with speakers attached to almost every column in the central aisle of the church. There are also speakers attached at the upper levels of the transepts, or wings of the church that form the cross shape, seen from above on the blueprint. 

“You are seeing multiple speakers on this drawing but it is not the same speaker over and over,” explains Schafer, as he points to the speakers on each column. “These are actually different locations down the nave and in the transepts, so there is no one loud speaker.” 

Acoustic engineers call it a distributed sound system, which means each speaker is throwing sound to only a small area and the speaker is aimed down, which directs the sounds and prevents it from reverberating all over the building. 

It all allows worshippers to hear heavenly sounds, scientifically helped. 

“You can think of a steerable loudspeaker as an umbrella which collapses downward all the way around,” says Schafer. “So now we are keeping the sound off the wall and off the ceiling and only on people right below who want to hear.” 

“We are taking great care with the sound because it is extremely important, so that that language can communicate through all of the senses,” says Monsignor David Brockman, the Vicar General of the Diocese who has worked closely on the cathedral project. “We want the faithful to not only experience our Lord in the beauty they see, but also in the words and music they hear.”

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